Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Andrew Michael Hawryluk. / Ph.D.

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The main subject of this thesis is the study of electronic and magnetic properties of materials containing 3d transition metal atoms. Our motivation stems mainly from the modern fields of spintronic computing and solar energy conversion. The two primary goals of this work are to determine (i) why certain transition metal impurities in certain semiconductors can induce magnetic properties suitable for spintronic computing applications, and (ii) how transition metal impurities can be used to modify the electronic band gaps of semiconductors and insulators in ways useful for harnessing solar energy and for other applications. To accomplish these goals, we have applied both experimental and theoretical tools. We studied high quality materials prepared by advanced synthesis techniques using x-ray spectroscopy methods at synchrotron light sources. The results of these experiments were interpreted using a variety of theoretical techniques, primarily using computational software developed as part of this thesis and discussed herein. Regarding the study of introducing transition metal impurities into semiconductors to induce magnetic properties, we first developed and demonstrated a method to determine the location of impurity atoms within the host semiconductor lattice. This allowed to us explain the presence and absence of ferromagnetism in samples prepared under only slightly different synthesis conditions, which helped to address some long--standing issues in the spintronics field. We then studied an advanced and promising material -- indium (III) oxide with iron impurities -- to determine how magnetic ordering was maintained up to room temperatures. Our techniques unveiled that a portion of the iron atoms were coupled to oxygen vacancies in the material to create conditions which propelled the observed magnetism. This finding confirmed some earlier theoretical predictions by others in the field. For the study of electronic band gap modifications in semiconductors and insulators via the incorporation of transition metal atoms, we investigated a wide range of materials synthesized using different techniques. Again, we used experimental techniques to determine the location of impurity atoms within the materials, and used this to understand how band gaps were modified upon the introduction of the impurities. For Ti implantation into SiO2, Ni substitution into ZnO, and a new material, MnNCN, we have determined the electronic band gaps and used our techniques to explain how the values for the gaps arise. Finally, an additional outcome of this thesis work is a software program capable of simulating x-ray spectra using various advanced quantum models. We rewrote and built upon powerful existing programs and applied the result to the above studies. Our software was further applied in a collaborative effort with other researchers at the Canadian Light Source to study the differences in two experimental techniques for measuring x-ray absorption: partial and inverse partial fluorescence yields. By using the proper absorption and scattering formalisms to simulate each technique, we were able to explain the differences between the experimental spectra obtained from each. We explain fluorescence yield deviations using an analysis based on the spin configuration of different states, suggesting that the technique can be further extended as a quantitative spin state probe. These results could have significant implications for the field of soft x-ray absorption spectroscopy.

A new gamma imaging method, Neutron Stimulated Emission Computed Tomography (NSECT), is being developed to non-invasively and non-destructively measure and image elemental concentrations in vivo. In NSECT a beam of fast neutrons (3 - 5 MeV) bombards a target, inelastically scattering with target nuclei and exciting them. Decay from this excited state produces characteristic gamma emissions. Collecting the resulting gamma energy spectrum allows identification of elements present in the target. As these gamma rays range in energy from 0.3 - 1.5 MeV, outside the useable energy range for existing gamma cameras (0.1 - .511 MeV), a new gamma imaging method must be developed. The purpose of this dissertation is to design and develop a near-field (less then 0.5 m) high-energy (0.3 - 1.5 MeV) gamma camera to facilitate planar NSECT imaging. Modifying a design implemented in space-based imaging (focus of infinity), a prototype camera was built. Experimental testing showed that the far-field space-based assumptions were inapplicable in the near-field. A new mathematical model was developed to describe the modulation behavior in the near-field. Additionally, a Monte Carlo simulation of the camera and imaging environment was developed. These two tools were used to facilitate optimization of the camera parameters. Simulated data was then used to reconstruct images for both small animal and human fields of view. Limitations of the camera design were identified and quantified. Image analysis demonstrated that the camera has the potential to identify regions of interest in a human field of view. / Dissertation

Thesis (M.S.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (leaves 86-88).

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 225-235). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 113-118).

published_or_final_version / Physics / Master / Master of Philosophy